Design and characterization of a novel pH-sensitive membrane peptide class

Drug delivery systems have gained significant interest in the pharmaceutical industry for the treatment of various diseases, such as cancer, neurological and genetic disorders, and viral infections. While many of the designed compounds show great potential by having a high affinity to their specific molecular targets in vitro, their potency is limited due to their failure to deliver molecules across the cell membrane. Their transporting ability is affected by their characteristics such as poor water solubility, charge, hydrophobicity, and size. Thus, there is a necessity for the design of new molecular transporters that can efficiently deliver molecules across the semi-permeable plasma membrane. Peptides have been studied rigorously as a drug delivery system due to several factors such as their capability to bind specific cell surface receptors, their ability to permeate through the hydrophobic core of the plasma membrane, and the ease of making small adjustments to the amino acid sequence. Furthermore, the major concern of targeting of a single molecular marker of the cancerous cell is tumor heterogeneity and rapid mutations. It is vital to focus on an intrinsic property of the diseased cell, such as the extracellular pH of cancer cells. For example, in malignant tumors, the extracellular pH can approximately be one pH unit lower than normal cells. A pH-triggered membrane peptide can be used to target cells with altered extracellular pH. Therefore, we have designed the acidity triggered rational membrane (ATRAM) peptide as a novel class of pH-sensitive peptides to address these applications. Here we established that the ATRAM peptide interacts in a pH-sensitive manner with membranes of liposomes and cultured cancer cells. ATRAM also interacts reversibly with human serum albumin suggesting that while the peptide can use albumin as a carrier in the blood stream, explaining its ability to avoid immediate proteolysis in vivo, it will still target and transfer to the cell membrane. Moreover, we tried to fine-tune the pH responsiveness of ATRAM. The subsequent single N-terminal modifications to the peptide sequence resulted in diverse interactions with cancer-mimic lipid vesicles